The invention relates to a monolithically integrated filter to process digitized signals, and in particular to a digital filter configurable with a plurality of basic units.
Monolithically integrated filters are used in digital signal processing for various tasks including signal extraction and signal formation. As known their advantages compared to analog filters include exact specification of their properties and lack of sensitivity to manufacturing tolerances, aging, temperature, interference, and other influences. As the number of functional units within a single monolithically integrated circuit increases, the number of digital filters used therein typically increases.
If the digital signals being processed have a low clock rate, a digital signal processor (DSP) can be programmed to yield the desired digital filter function. Such filter realizations are especially advantageous where the filter properties must be matched to specific signal standards (e.g., with a multi-standard receiver for television or audio signals). Configuring the DSP to match the different standards is relatively easy since the configuration is set by the executable code associated with the DSP. Without such programming, a special static filter set would always be required for different standards. The different programs also make it possible to switch back and forth between different filter functions (e.g., between a low-pass and a high-pass function).
However, digital signal processors cannot be used when the data rates being processed are too high for the particular signal processor. For example, with a frequency above 5 MHz, the speed of the current processors is too slow, and therefore parallel hardware architectures must be used for filter realization. However, such hardware architectures consume much space in monolithically integrated circuits. The desired flexibility consequently must be purchased expensively by furnishing parallel structures, of which only a single one is always in operation.
Therefore, there is a need for a flexible (i.e., programmable) filter that can process digital signals with a high data rate and can be monolithically integrated.